INTRODUCTION: Uterine ribosomal RNA synthesis by uterine nucleoli is stimulated early and remains elevated following estradiol treatment. The precise mechanism by which estradiol stimulates uterine ribosomal RNA synthesis remains to be determined and the overall role of nucleolar RNA synthesis, in addition to providing ribosomal RNA, in the estrogen stimulation of uterine growth is unclear. OBJECTIVES: 1) To characterize the physiological and pharmacological effect of in vivo administration of estradiol on the synthesis of RNA by isolated uterine nucleoli, 2) To determine the molecular mechanism by which in vivo administration of estradiol stimulates nucleolar RNA synthesis in isolated uterine nucleoli, 3) To determine the nature of the protein(s) which is (are) essential for enhanced uterine ribosomal RNA synthesis, 4) To determine the role of the steroid-receptor complex in the stimulation of RNA synthesis by uterine nucleoli, and 5) To determine the relationship between estrogen induced necleolar RNA synthesis and stimulation of uterine cellular proliferation by in vivo administration of estradiol. SIGNIFICANCE: Hormones are known to control growth, metabolism and differentiation in target tissues but the means by which these effects are achieved remains incompletely defined. Regulation of gene transcription has been postulated as the mechanism for control of target tissue development. Estradiol administration to ovariectomized mature rats causes an early preferential increase in uterine ribosomal RNA content and recent observations in other tissues suggest that stimulation of nucleolar (ribosomal?) RNA synthesis may be tightly coupled in a cause and effect relationship to other growth related processes including DNA synthesis in this tissue. The study should provide a better understanding of the mechanisms of control of transcription and a better understanding of growth control of normal tissues derived from this study may have application to abnormal type cells (cancer cells).